Download Today, we will explain how an air mass forms.

Journal #44
1. How often do you watch the weather on
TV/internet? Why?
2. What kinds of weather or weather conditions are
there?
3. Can you name situations in which weather has
impacted your life or affected your plans? Explain.
4. What kinds of elements, things, or conditions
influence the weather?
5. Why is the study of weather important? Offer
examples.
6. Why do people in general pay little attention to
the weather?
7. Do you think this is a good idea? Why or why not?
Today, we will explain how an air
mass forms.
Air Masses
• Differences in air pressure
– What causes these differences?
• Wind patterns
– Caused by differences in air pressure.
• Video
– Characteristics of Air Masses
How Air Moves
• Air moves from high pressure to areas of low
pressure.
• Surface air from the poles moves toward the
equator.
• At high altitudes, warm air from the equator
moves toward the poles.
• Temperature and pressure differences create 3
wind belts in the Northern hemisphere and 3
in the southern.
The Coriolis Effect
• The Coriolis effect occurs when winds are
deflected by Earth’s rotation.
• The Coriolis effect also influences wind
patterns.
• The processes that affect air movement also
influence storms.
Formation of Air Masses
• When air pressure differences are small, air
remains stationary (in place) or moves slowly.
• If the air remains stationary, the air takes on
characteristic temperatures and humidity of that
region.
• A large body of air throughout which
temperature and moisture are similar is called an
air mass.
– What are air masses like over polar regions?
– What about air masses over tropical regions
Types of Air masses
• Air masses are classified according to their source
regions.
– Temperature
– Humidy
• The source regions for warm air masses are tropical
areas
• The source regions for cool air masses are polar areas.
• Air masses that form over oceans are called maritime.
• Air masses that form over land are called continental.
Types of Air Masses (cont)
• Maritime air masses are moist and continental
air masses are dry.
• Air masses symbols:
–
–
–
–
Continental- c
Maritime- m
Tropical- T
Polar-P
• Combinations of air results in air masses with
distinct characteristics.
Continental Air Masses
• These air masses form over large landmasses
(northern Canada, northern Asia,
southwestern US)
• Form over land so the humidity is low.
• The air mass will eventually move into other
regions because of global wind patterns.
• They bring dry weather conditions
Types of Continental Air Masses
• There are 2 types of continental air masses:
– Continental polar (cP)- cold and dry
– Continental tropical (cT)- warm and dry
Maritime Air Masses
• Maritime air masses form over oceans or
other large bodies of water.
• Humidity of these air masses tends to be
higher than continental air masses
• When theses humid air masses travel they
bring more precipitation and fog
Types of Maritime Air Masses
• There are 2 types of maritime air masses
– Maritime polar (mP)- moist and cold
– Maritime tropical (mT)- moist and warm
Air Masses
Source- Region of
Air Mass
Continental Polar
Continental
Tropical
Maritime
Tropical
Maritime Polar
Type of Air
(Weather)
Symbol
Colored Picture:
(blue=cold)
(red=warm)
North American Air Masses
• The four types of air masses that affect the
weather of North America come from 6
regions.
• An air mass usually brings the weather of its
source region, but may change as it moves
away.
• Example: What will happen if cold dry air
moves towards warm ocean?
– What weather would you expect?
Your assignment:
• Air Masses Activity
Air Mass #1
Air Mass #1
• Those who live in northern portions of the United
States expect cold weather during the winter months.
• These conditions usually result from the invasion of
cold arctic air masses that originate from the snow
covered regions of northern Canada.
• Because of the long winter nights and strong
radiational cooling found in these regions, the
overlying air becomes very cold and very stable.
• The longer this process continues, the colder the
developing air mass becomes, until changing weather
patterns transport the arctic air mass southward.
Air Mass #2
Air Mass #2
• Maritime Tropical Air Masses- Warm
temperatures and rich in moisture
• Maritime tropical air masses originate over the
warm waters of the tropics and Gulf of Mexico,
where heat and moisture are transferred to the
overlying air from the waters below.
• The northward movement of tropical air masses
transports warm moist air into the United States,
increasing the potential for precipitation.
Review:
• What are the characteristics of maritime
tropical air masses? Where do they originate?
How do they affect weather?
– (The characteristics are warm temperatures, rich
in moisture. They originate over the warm waters
of the tropics and Gulf of Mexico. The northward
movement of tropical air masses transports warm
moist air into the United States, increasing the
chances of precipitation.)
Review:
• What is a continental polar air mass? Where
does it originate? How does it affect weather?
– It is an air mass with cold temperatures and little
moisture. It originates in snow-covered regions of
northern Canada. It affects weather by turning it
colder.
• In your own words, describe the role that air
masses play in weather.
Review:
• What was the most challenging part of
mapping out air masses?
• How, if any, has this lesson affected your view
of weather?